The present invention relates to data storage systems, and more particularly, this invention relates to selectively writing an index on a magnetic recording tape.
In magnetic storage systems, magnetic transducers read data from and write data onto magnetic recording media. Data is written on the magnetic recording media by moving a magnetic recording transducer to a position over the media where the data is to be stored. The magnetic recording transducer then generates a magnetic field, which encodes the data into the magnetic media. Data is read from the media by similarly positioning the magnetic read transducer and then sensing the magnetic field of the magnetic media. Read and write operations may be independently synchronized with the movement of the media to ensure that the data can be read from and written to the desired location on the media.
An important and continuing goal in the data storage industry is that of increasing the density of data stored on a medium. For tape storage systems, that goal has led to increasing the track and linear bit density on recording tape, and decreasing the thickness of the magnetic tape medium. However, the development of small footprint, higher performance tape drive systems has created various problems in the design of a tape head assembly for use in such systems.
In a tape drive system, the drive moves the magnetic tape over the surface of the tape head at high speed. Usually the tape head is designed to minimize the spacing between the head and the tape. The spacing between the magnetic head and the magnetic tape is crucial and so goals in these systems are to have the recording gaps of the transducers, which are the source of the magnetic recording flux in near contact with the tape to effect writing sharp transitions, and to have the read elements in near contact with the tape to provide effective coupling of the magnetic field from the tape to the read elements.
Another important and continuing goal in the data storage industry is that of decreasing the time and/or number of operations used when performing a given task within a tape drive system. For example, because stiction tends to occur between the tape and a magnetic tape head of a tape drive when the tape drive system is idle with a threaded tape therein, conventional tape drive systems often unthread magnetic tape that has not been accessed in a predetermined amount of time. Stiction has been known to be so strong that the tape may break rather than separate from the head. The unthreading is performed in an effort to prevent the stiction from forming. However, the tape remains loaded in the tape drive system and “mounted” for further operations until an unload and/or unmount command is received.
Because the index or indexes of the location of data written to a magnetic tape are not updated by the tape drive system prior to this unthreading, in the event that an unload and/or unmount command is received by the tape drive system while the tape is unthreaded, the tape must be rethreaded for recording such indexes. Moreover, depending on the indexing scheme used, much of the tape may need to be traversed to arrive at the location where the index is to be written, e.g., such as at the end of the last written data. This exacerbates the time required to write the index.
If the tape is not rethreaded to record such index, the index location of previously written data may be lost, which would require the tape drive system to parse the tape to find the data upon a subsequent loading of the tape. This parsing of the tape is undesirably time consuming.
Accordingly, conventional tape drive systems suffer from having to rethread a tape for indexing in response to receiving an unload and/or unmount command while the tape is unthreaded. Such rethreading to simply write index information is a time-consuming process, which affects the overall efficiency of the data storage system of which the tape drive system is a part. Conventional tape drive systems that do not rethread an unthreaded tape to write an index in a data partition of the tape may require a time-consuming reparsing of the tape when accessing data that was not adequately indexed.